.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
.\"
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.TH GETPID 2 2015-07-23 "Linux" "Linux Programmer's Manual"
.SH NAME
getpid, getppid \- get process identification
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <unistd.h>
.sp
.B pid_t getpid(void);
.br
.B pid_t getppid(void);
.SH DESCRIPTION
.BR getpid ()
returns the process ID of the calling process.
(This is often used by
routines that generate unique temporary filenames.)

.BR getppid ()
returns the process ID of the parent of the calling process.
.SH ERRORS
These functions are always successful.
.SH CONFORMING TO
POSIX.1-2001, POSIX.1-2008, 4.3BSD, SVr4.
.SH NOTES
If the caller's parent is in a different PID namespace (see
.BR pid_namespaces (7)),
.BR getppid ()
returns 0.
.\"
.SS C library/kernel differences
Since glibc version 2.3.4,
the glibc wrapper function for
.BR getpid ()
caches PIDs,
so as to avoid additional system calls when a process calls
.BR getpid ()
repeatedly.
Normally this caching is invisible,
but its correct operation relies on support in the wrapper functions for
.BR fork (2),
.BR vfork (2),
and
.BR clone (2):
if an application bypasses the glibc wrappers for these system calls by using
.BR syscall (2),
then a call to
.BR getpid ()
in the child will return the wrong value
(to be precise: it will return the PID of the parent process).
.\" The following program demonstrates this "feature":
.\"
.\" #define _GNU_SOURCE
.\" #include <sys/syscall.h>
.\" #include <sys/wait.h>
.\" #include <stdio.h>
.\" #include <stdlib.h>
.\" #include <unistd.h>
.\"
.\" int
.\" main(int argc, char *argv[])
.\" {
.\"    /* The following statement fills the getpid() cache */
.\"
.\"    printf("parent PID = %ld\n", (long) getpid());
.\"
.\"    if (syscall(SYS_fork) == 0) {
.\"        if (getpid() != syscall(SYS_getpid))
.\"            printf("child getpid() mismatch: getpid()=%ld; "
.\"                    "syscall(SYS_getpid)=%ld\n",
.\"                    (long) getpid(), (long) syscall(SYS_getpid));
.\"        exit(EXIT_SUCCESS);
.\"    }
.\"    wait(NULL);
.\"}
See also
.BR clone (2)
for discussion of a case where
.BR getpid ()
may return the wrong value even when invoking
.BR clone (2)
via the glibc wrapper function.
.SH SEE ALSO
.BR clone (2),
.BR fork (2),
.BR kill (2),
.BR exec (3),
.BR mkstemp (3),
.BR tempnam (3),
.BR tmpfile (3),
.BR tmpnam (3),
.BR credentials (7),
.BR pid_namespaces (7)
